JP2022009843A - Positive electrode active material and lithium secondary battery including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material having improved structural stability and improved lithium ion conductivity, and a lithium secondary battery using a positive electrode including the positive electrode active material.

SOLUTION: A positive electrode active material includes a first composite oxide capable of occluding and releasing lithium, and a second composite oxide present on at least a part of the surface of the first composite oxide, and the first composite oxide and the second composite oxide exist in a state of forming a solid solution, and the second composite oxide is represented by Li_aM1_bM2_cO_d, and here, M1 is at least one selected from Ni, Mn, Co, Cu, Nb, Mo, Al, Zn, Mg, Ce, and Sn, and M2 is Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd, and Gd, and M1 and M2 are different from each other, and 0≤a≤6, 0<b≤2, 0<c≤2, and 4≤d≤8 are satisfied.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode containing the positive electrode active material.

A battery stores electric power by using a substance capable of an electrochemical reaction between a positive electrode and a negative electrode. A typical example of such a battery is a lithium secondary battery that stores electrical energy by the difference in chemical potential when lithium ions are intercalated / deintercalated at the positive and negative electrodes. There is.

The lithium secondary battery uses a substance capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and an organic electrolytic solution or a polymer electrolytic solution is used between the positive electrode and the negative electrode. Is filled and manufactured.

Lithium composite oxides are used as the positive electrode active material of the lithium secondary battery, and composite oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiMnO ₂ have been studied as examples.

Among the positive electrode active materials, LiCoO ₂ is most often used because it has excellent life characteristics and charge / discharge efficiency, but it is expensive due to the resource limitation of cobalt used as a raw material. It has the disadvantage of limited competitiveness.

Lithium manganese oxides such as LiMnO ₂ and LiMn _{2O 4} have advantages of excellent thermal safety and low price, but have problems of small capacity and poor high temperature characteristics. In addition, the LiNiO ₂ -based positive electrode active material exhibits high discharge capacity battery characteristics, but is difficult to synthesize due to the problem of cation mixing between Li and the transition metal, and thus the rate. There is a big problem with the characteristics.

In addition, a large amount of Li by-products will be generated depending on the degree of deepening of such cation mixing, and most of these Li by-products are composed of compounds of LiOH and Li ₂ CO ₃ , so that during the production of the positive electrode paste, It causes the problem of gelling and the generation of gas due to the progress of charging and discharging after the electrode is manufactured. The residual Li ₂ CO ₃ increases the swelling phenomenon of the cell, reduces the cycle, and causes the battery to swell.

Korean Publication No. 10-2015-0069334 Gazette

An object of the present invention is to provide a positive electrode active material having improved structural stability and improved lithium ion conductivity in order to solve various problems of existing positive electrode active materials for lithium secondary batteries. It is in.

Another object of the present invention is to provide a positive electrode active material having improved high temperature storage stability and life characteristics by containing a heterogeneous composite oxide as defined in the present application.

Another object of the present invention is to provide a lithium secondary battery using a positive electrode containing a positive electrode active material as defined in the present application.

The object of the present invention is not limited to the object mentioned above, and other purposes and advantages of the present invention not mentioned may be understood by the following description and further clearly understood by the examples of the present invention. right. In addition, it can be easily known that the object and the advantage of the present invention can be realized by the means and combinations thereof shown in the claims.

According to one aspect of the present invention, the first composite oxide capable of sucking and releasing lithium and the first composite oxide present on at least a part of the surface of the first composite oxide, and the first composite oxide and a solid solution are formed. A positive electrode active material containing a second complex oxide that exists in the formed state can be provided.

At this time, the second composite oxide is represented by the following chemical formula 1.

[Chemical formula 1]
Li _a M1 _b M2 _{c Od}

(Here, M1 is at least one selected from Ni, Mn, Co, Cu, Nb, Mo, Al, Zn, Mg, Ce and Sn, and M2 is Mn, Al, Ti, Zr, Mg. , V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd, and M1 and M2 are different from each other and 0 ≦ a ≦ 6, 0 <b ≦ 2, 0 <c ≦ 2, 4 ≦ d ≦ 8)

Further, according to another aspect of the present invention, a lithium secondary battery using a positive electrode containing a positive electrode active material as defined in the present application can be provided.

The positive electrode active material according to various examples of the present invention contains a heterogeneous composite oxide, and in particular, the second composite oxide forms a solid solution with at least a part of the first composite oxide to form a solid solution. Question Structural stability and thermal stability (high temperature storage stability) can be improved.

Further, as the positive electrode active material having the above-mentioned structure improves the lithium ion conductivity in the active material, the electrochemical characteristics such as the life characteristic, the efficiency characteristic and the resistance of the positive electrode active material also become the conventional positive electrode active material. Can be improved in comparison.

Along with the above-mentioned effects, the specific effects of the present invention will be described together with the following explanation of specific matters for carrying out the invention.

It is a figure which shows the result of the transmission electron microscope (TEM) analysis on one surface of the positive electrode active material produced by one Example of this invention. It is a figure which shows the XPS analysis result with respect to the positive electrode active material produced by one Example of this invention. It is a graph which shows the XRD analysis result with respect to the positive electrode active material produced by one Example of this invention. It is a graph which shows the XRD analysis result with respect to the positive electrode active material produced by one Example of this invention. It is a graph which shows the XRD analysis result with respect to the positive electrode active material produced by one Example of this invention. It is a graph which shows the XRD analysis result with respect to the positive electrode active material produced by another Example of this invention. It is a graph which shows the XRD analysis result with respect to the positive electrode active material produced by another Example of this invention. It is a graph which shows the XRD analysis result with respect to the positive electrode active material produced by another Example of this invention.

For convenience, specific terms are defined herein in order to better understand the invention. Unless otherwise defined herein, the scientific and technical terms used in the present invention have the meaning generally understood by those with ordinary knowledge in the art. Further, unless otherwise specified in the context, the term in the singular form shall be understood to include the plural form thereof, and the term in the plural form shall be understood to include the singular form as well.

Hereinafter, the positive electrode active material according to the present invention and the lithium secondary battery using the positive electrode containing the positive electrode active material will be described in more detail.

Positive Electrode Active Material According to one aspect of the present invention, it contains a first composite oxide capable of absorbing and releasing lithium and a second composite oxide present on at least a part of the surface of the first composite oxide. Positive electrode active material may be provided.

At this time, the first composite oxide and the second composite oxide in the positive electrode active material can exist in a state where a solid solution is formed.

For example, when the first composite oxide is referred to as A and the second composite oxide is referred to as B, the solid solution formed by the first composite oxide and the second composite oxide is (AB) _p or (). A) _q (B) may be in the _r form.

However, the solid solution referred to in the present application is a solid solution in the form of (A) _q (B) _r , and here, the (A) _q portion corresponds to the core of the primary particles forming the positive electrode active material, and ( B) The _r portion can correspond to the shell of the primary particles forming the positive electrode active material. Along with this, in the solid solution of the first composite oxide and the second composite oxide, which is meant in the present application, the core containing the first composite oxide and the shell layer containing the second composite oxide are in the form of a solid solution. It must be understood to refer to existing core-shell particles. At this time, the shell layer can be present so as to cover a part or all of the surface of the core, and the second composite oxide is present in a part or all of the shell layer. Can be done. Here, the second composite oxide existing in the shell layer can also be understood to mean a region corresponding to the second composite oxide in the solid solution.

As described above, the solid solution formed by the first composite oxide and the second composite oxide exists in the form of core-shell particles, and the core-shell particles are spherical, rod-shaped, elliptical and elliptical. / Or can have an amorphous shape.

Further, the positive electrode active material is a single secondary particle itself formed by agglomeration of the core-shell particles and the core-shell particles, or is formed by a plurality of the secondary particles gathered together. It may be an aggregate.

The second complex oxide defined in the present application can be defined as a particle represented by the following chemical formula 1. The following chemical formula 1 is described for independently specifying the second composite oxide mentioned in the present application, and the second composite oxide present in the positive electrode active material according to one aspect of the present invention is the first. When a solid solution is formed with one composite oxide, it is represented by the chemical formula 3 described later.

[Chemical formula 1]
Li _a M1 _b M2 _{c Od}

(here,
M1 is at least one selected from Ni, Mn, Co, Cu, Nb, Mo, Al, Zn, Mg, Ce and Sn.
M2 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
M1 and M2 are different from each other
0 ≦ a ≦ 6, 0 <b ≦ 2, 0 <c ≦ 2, 4 ≦ d ≦ 8. )

More specifically, M1 may be at least one selected from Mn, Mg, Co and Ni.

For example, when M1 is Ni and M2 is W, the second composite oxide is represented by the chemical formula _{Lia Ni b W c Od} . Further, when M1 is Co and M2 is W, the second composite oxide is represented by the chemical formula Li _a Co _b W _{c Od} . When M1 is Mn and M2 is W, the second composite oxide is represented by the chemical formula Li _a Mn _b W _{c Od} . When M1 is Mg and M2 is W, the second composite oxide is represented by the chemical formula Li _a Mg _b W _{c Od} .

At this time, the second composite oxide is a composite oxide represented by the chemical formula Li _a Ni _b W _{c Od} , a composite oxide represented by the chemical formula Li _a Co _b W _{c Od} , and a chemical formula Li _a Mn _b W. It means one composite oxide selected from the composite oxide represented by _c Od and the composite oxide represented by the chemical formula Li _a Mg _b W _{c Od} , or in Li _a Ni _b W _c O _{d .} The composite oxide represented by the chemical formula Li _a Co _b W _{c Od} , the composite oxide represented by the chemical formula Li _a Mn _b W _{c Od} , and the chemical formula Li _a Mg _b W _{c Od.} It is also possible to simultaneously contain a plurality of composite oxides selected from the composite oxides represented by. Here, the composite oxide represented by Li _a Ni _b W _{c Od} is a composite oxide represented by Li ₄ NiWO ₆ , Li ₃ Ni WO ₆ and / or Li ₂ Ni (WO ₄ ) ₂ . It may be, but it is not always limited to these.

Further, in another embodiment, M1 in the chemical formula 1 displaying the second composite oxide may be a different kind of metal element. For example, the second composite oxide is a composite oxide represented by the chemical formula Li _a (Ni + Co) _b W _{c Od} , a composite oxide represented by the chemical formula Li _a (Ni + Mn) _b W _c O _d , and a chemical formula Li _a . (Ni + Mg) means one composite oxide selected from the composite oxide represented by _b W _{c Od, or a composite oxide represented by the chemical formula Li a Ni b W c O d , the chemical formula} Li _a Co. _b Composite oxide represented by W _{c Od} , composite oxide represented by chemical formula Li _a Mn _b W _{c Od} , composite oxide represented by chemical formula Li _a Mg _b W _c O _d , chemical formula Li _a (Ni + Co) Composite oxide represented by _b W _{c Od} , composite oxide represented by chemical formula Li _a (Ni + Mn) _b W _c O _d , and chemical formula Li _a (Ni + Mg) _b W _c O _d . Any combination of composite oxides selected from the composite oxides can also be included at the same time.

As described above, on the premise that the second composite oxide can form a solid solution with the first composite oxide to improve the structural and thermal stability of the positive electrode active material. It can have various compositions depending on the type of M1 and M2.

At this time, the second composite oxide may have the same or different crystal structure as the first composite oxide. For example, the second complex oxide can have at least one crystal structure selected from monoclinic, triclinic and cubic. Further, the second composite oxide present in the shell layer may be a lithium-rich metal oxide.

As a specific example, the second composite oxide having a monoclinic crystal structure in which M1 is Ni and M2 is W is represented by the chemical formula _{Lia Ni b W c Od} and is triclinic. The second complex oxide having a crystal structure is represented by the chemical formula Li _a Ni _b (W _c O _d ) ₂ .

On the other hand, in the SEM or TEM photograph of the positive electrode active material, the core and the shell layer may be difficult to be separated with a clear boundary, but in the present application, the positive electrode activity is used to help understanding the contents described in the present specification. The structure of the material will be explained separately for the core and shell layers.

That is, in the present application, the core may be defined as a region in which the first composite oxide is present, and the shell layer may be defined as a region in which the second composite oxide is present, and the first composite oxide and the second composite oxide are present. The thickness or size of the core and shell layers can vary depending on the depth of the area to be covered.

At this time, the thickness of the shell layer may be 20 nm, preferably 10 nm, more preferably 5 nm or less, but is not necessarily limited to these.

It must also be understood that if the shell layer is present on a portion of the surface of the core, the first composite oxide can also be exposed to the outside on the surface of the core without the shell layer.

The first complex oxide defined in the present application can be defined as a particle represented by the following chemical formula 2.

[Chemical formula 2]
Li _w Ni _{1- (x + y + z)} Co _x M3 _y M4 _z O ₂

(here,
M3 is at least one selected from Mn and Al,
M4 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
0.5 ≦ w ≦ 1.2, 0.01 ≦ x ≦ 0.50, 0.01 ≦ y ≦ 0.20, 0.001 ≦ z ≦ 0.20. )

The core-shell particles can contact adjacent core-shell particles with each other to form an interface or grain boundary between the core-shell particles. In addition, the core-shell particles can also form internal pores inside the secondary particles separated from adjacent core-shell particles.

Here, the average diameter of the core-shell particles may be 0.1 μm to 6.0 μm, and the average diameter of the secondary particles may be 6.0 μm to 20.0 μm. At this time, the core-shell particles do not contact each other with adjacent core-shell particles to form crystal grain boundaries, but form a surface existing inside the secondary particles by contacting with internal pores. Can be done. On the other hand, the surface of the core-shell particles present on the outermost surface of the secondary particles exposed to the outside air forms the surface of the secondary particles.

Further, M2 and / or M4 contained in the core-shell particles present on the surface portion of the secondary particles can show a concentration gradient that decreases toward the central portion of the secondary particles. That is, the direction of the concentration gradient of M2 and / or M4 formed in the core-shell particles may be the direction from the surface portion of the secondary particles toward the center portion of the secondary particles.

More specifically, the concentration gradient of M2 and / or M4 contained in the core-shell particles is the concentration gradient of the secondary particles from the central portion side of the secondary particles with reference to the central portion of the core-shell particles. It may be large on the surface side.

In this case, the secondary particles can include a first region and a second region in which the concentrations of M2 and / or M4 are different from each other.

Here, the region showing a concentration gradient in which M2 and / or M4 contained in the core-shell particles decreases toward the center of the secondary particles may be the first region. That is, the concentration gradient of M2 and / or M4 defined in the present application means a concentration gradient that appears with respect to a single core-shell particle.

For example, when the distance from the outermost surface of the secondary particles forming the lithium composite oxide to the center of the secondary particles is R, the distance R'from the outermost surface of the secondary particles is 0 to 0.02 R. When the region is defined as the first region, M2 and / or M4 existing in the first region show a concentration gradient that decreases toward the center of the secondary particles in the core-shell particles. Can be done.

On the other hand, Ni present in the first region can show a concentration gradient increasing toward the center of the secondary particles in the core-shell particles, contrary to M2 and / or M4. Here, the central portion of the secondary particles can point to the center of the secondary particles.

At this time, the concentration change rate of M2 and / or M4 contained in the core-shell particles existing in the first region may be 50% or more, preferably 60% or more, but this is always the case. It is not limited to.

Further, the remaining region excluding the first region can be defined as the second region, and the region where the distance R'from the outermost surface of the secondary particles is 0 to 0.02R is defined as the first region. The region where the distance R'from the outermost surface of the secondary particles is more than 0.02R and 1.0R can be defined as the second region. Here, M2 and / or M4 contained in the core-shell particles existing in the second region have a concentration gradient in a form in which the concentration increases or decreases in a certain direction in the core-shell particles. You don't have to.

In another embodiment, the concentration change rate of M2 and / or M4 in the core-shell particles present in the second region is 49% or less, preferably 30% or less, more preferably 15% or less. May be good.

Further, in this case, the concentration change rate of Co and M3 contained in the core-shell particles existing in the first region and the second region is 49% or less, preferably 30% or less, more preferably 15. It may be less than or equal to%.

As described above, the secondary particles constituting the lithium composite oxide are divided into a first region and a second region in which the concentrations of M2 and / or M4 are different from each other, and M2 and / or M4 is the first region. And by showing different modes of concentration gradient within the second region, the structural stability and thermal stability (high temperature storage stability) of the lithium composite oxide can be improved.

In addition, as the lithium ion conductivity in the active material is improved, the positive electrode active material including the core having the above-mentioned concentration gradient also has the conventional electrochemical characteristics such as the life characteristic, the efficiency characteristic and the resistance of the positive electrode active material. It can be improved as compared with the positive electrode active material of.

As described above, the second composite oxide present on at least a part of the surface of the first composite oxide can exist in a state of forming a solid solution with the first composite oxide.

Here, the solid solution is represented by the following chemical formula 3.

[Chemical formula 3]
Li _a M1 _b M2 _{c Od} -Li _w Ni _{1- (x + y + z)} Co _x M3 _y M4 _z O ₂

(here,
M1 is at least one selected from Ni, Mn, Co, Cu, Nb, Mo, Al, Zn, Mg, Ce and Sn.
M2 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
M3 is at least one selected from Mn and Al,
M4 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
M1 and M2 are different from each other
0 ≦ a ≦ 6, 0 <b ≦ 2, 0 <c ≦ 2, 4 ≦ d ≦ 8
0.5 ≦ w ≦ 1.5, 0.01 ≦ x ≦ 0.50, 0.01 ≦ y ≦ 0.20, 0.001 ≦ z ≦ 0.20. )

More specifically, M2 may be identical to a portion of M4 or M4. That is, when M2 and M4 are single elements, M2 and M4 may be the same, and when M2 and M4 are each a plurality of elements, all or part of M2 is all or part of M4. May be the same as.

Here, when all or part of M2 is the same as all or part of M4, M2 and M4 have a concentration gradient that decreases from the surface portion of the positive electrode active material toward the center of the positive electrode active material. Can be done.

In another embodiment, the solid solution is represented by the following chemical formula 3-1.

[Chemical formula 3-1]
Li _a M1 _b W _{c Od} -Li _w Ni _{1- (x + y + z)} Co _x M2 _y M3 _z O ₂

(here,
M1 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V. , Ba, Ta, Sn, Hf, Ce, Gd and Nd.
M2 is at least one selected from Mn and Al,
M3 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
0 ≦ a ≦ 6, 0 ≦ b ≦ 2, 0 ≦ c ≦ 2, 4 ≦ d ≦ 8, 0.5 ≦ w ≦ 1.5, 0.01 ≦ x ≦ 0.50, 0.01 ≦ y ≦ 0.20, 0.001 ≦ z ≦ 0.20. )

Here, M3 can be W or can include W. That is, when M3 is a single element, M3 is W, while when M3 is a plurality of elements, M3 can contain W and non-W elements. When M3 is W or contains W, the elements W and non-W (if present) have a concentration gradient that decreases from the surface of the positive electrode active material towards the center of the positive electrode active material. Can be done.

The presence or absence of the solid solution represented by the chemical formula 3 and / or the chemical formula 3-1 in the positive electrode active material can be confirmed through XPS analysis, Raman shift analysis and / or XRD analysis results and the like.

In the case of the XRD analysis result, when the lithium composite oxide in the form of a solid solution represented by the chemical formula 3 and / or the chemical formula 3-1 is present, the solid solution is the first composite oxide and the second composite oxide. Diffraction peak characteristics can be shown at the same time.

For example, in a solid solution represented by the chemical formula 3, a second complex oxide in which M1 is Ni and M2 is W and a first composite oxide in which M3 is Al and M4 is W form a solid solution. , The solid solution is represented by the chemical formula Li _a Ni _b W _{c Od} -Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ , where the solid solution is specific to Li _a Ni _b W _c O _d . Diffraction peak characteristics and Li _w Ni 1- (x + _{y + z)} Co _x Aly W _z O ₂ specific diffraction peak characteristics can be exhibited at the same time.

Further, in the solid solution represented by the chemical formula 3-1 when the second complex oxide in which M1 is Ni and the first composite oxide in which M2 is Al and M3 is W form a solid solution, the solid solution is: The chemical formula Li _a Ni _b W _{c Od} -Li _w Ni _{1- (x + y + z)} is represented by Co _x Al _y W _z O ₂ , in which the solid solution is a diffraction peak specific to Li _a Ni _b W _{c Od} . Characteristics and Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ specific diffraction peak characteristics can be exhibited at the same time.

In this case, the solid solution form of the lithium composite oxide represented by the chemical formula 3 and / or the chemical formula 3-1 is used in XRD (X-ray diffraction) analysis using CuKα rays for the lithium composite oxide. The X-ray diffraction spectrum corresponds to the peak corresponding to the (001) crystal plane and the (003) crystal plane in the range of 2θ = 15 ° to 20 ° and the (104) crystal plane in the range of 2θ = 44 ° to 50 °, respectively. Can have a peak. Further, the lithium composite oxide in the solid solution form represented by the above chemical formulas 3 and / or chemical formula 3-1 has a peak corresponding to the (20-2) crystal plane in the range of 2θ = 42 ° to 44 °. Can be done.

Further, the lithium composite oxide in the form of a solid solution represented by the chemical formula 3-1 is Li _a Ni _b W _c at the peak for W4f and O1s during XPS (X-ray photoelectron spectroscopy) analysis for the lithium composite oxide. It is possible to simultaneously show peak characteristics specific to _Od and peak characteristics specific to Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ .

Specifically, at the time of XPS analysis for the lithium composite oxide, the peak corresponding to W4f _7/2 can be present in the range of 35.5 eV or less, preferably 34.0 eV to 35.0 eV.

Further, during the XPS analysis of the lithium composite oxide, the peak corresponding to W4f _7/2 can be present in the range of 37.5 eV or less, preferably 36.0 eV to 37.0 eV.

The W4f _7/2 peak for W ⁶⁺ of the oxide of Li _a Ni _b W _{c Od} composition is in the range of 34.0 eV to 35.0 eV, and the W4f _5/2 peak is 36.0 eV to 37. It can be in the range of 0 eV. On the other hand, the W4f _7/2 peak with respect to O ^2- of the oxide of Li _a W _{c Od} or W _{c Od} composition exists in the range exceeding 35.0 eV, and the W4f _5/2 peak is 37.0 eV. It can be confirmed that it exists in the range exceeding.

Therefore, at the time of XPS analysis for the lithium composite oxide contained in the positive electrode active material according to the embodiment of the present invention, a W4f _7/2 peak exists in the range of 34.0 eV to 35.0 eV, and 36.0 eV to 36.0 eV. By the presence of the W4f _5/2 peak within the range of 37.0 eV, the lithium composite oxide exhibits a peak peculiar to Li _a Ni _b W _{c Od} .

Further, during XPS analysis of the lithium composite oxide, peaks corresponding to O1s can be present in the range of 528.0 eV to 530.0 eV and the range of 530.0 eV to 531.0 eV, respectively.

The peak for the OM ^{3 +} bond of the oxide composition of Li _w Ni 1- (x + _{y + z)} Co _x Aly W _z O ₂ appears in the range of 528.0 eV to 529.0 eV. The peak of the oxides of Li _a Ni _b W _{c Od} composition with respect to O ^2- exists in the range of 530.0 eV to 531.0 eV, but the oxides of Li _a W _{c Od} and W _{c Od} compositions also exist. , Since the peak for O ^2- appears in the range of 530.0 eV to 531.0 eV, it may be difficult to distinguish each oxide.

The lithium composite oxide contained in the positive electrode active material according to an embodiment of the present invention is an oxide having a composition of Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ in the O1s spectrum at the time of XPS analysis. It is possible to simultaneously have a peak for O ^-2- of the oxide of Li _a Ni _b W _{c Od} composition with a peak corresponding to the ^{OM 3 +} bond of. The peak in the range of 530.0 eV to 531.0 eV may be due to the alloy oxide described later.

As described above, the positive electrode active material containing the solid solution represented by the above chemical formulas 3 and / or chemical formula 3-1 is active as the positive electrode activity is improved as the lithium ion conductivity in the active material, particularly on the surface of the active material is improved. Electrochemical properties such as life properties, efficiency properties and resistance of the material can also be improved as compared to conventional positive electrode active materials.

Further, in another embodiment, the positive electrode active material can include a coating layer that covers at least a part of the primary particles and / or the secondary particles formed by agglomeration of the primary particles.

For example, the coating layer can be present to cover at least a portion of the exposed surface of the core-shell particles, which are the primary particles. In particular, the coating layer can be present so as to cover at least a portion of the exposed surface of the core-shell particles, which are the primary particles present in the outermost shell of the secondary particles.

The coating layer thus present can contribute to the improvement of the physical and electrochemical properties of the positive electrode active material.

At this time, when the shell layer covers a part of the surface of the core in the core-shell particles which are the primary particles existing in the outermost part of the secondary particles, the coating layer is covered by the shell layer. It can be present to cover at least a portion of the surface of the core that is not, or to cover at least a portion of the shell layer.

Further, the coating layer can be defined as a region in which an alloy oxide represented by the following chemical formula 4 is present.

[Chemical formula 4]
Li _e M5 _{f Og}

(here,
M5 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. And
0 ≦ e ≦ 6, 0 <f ≦ 6, 0 <g ≦ 10. )

The alloy oxide may be in a state of being physically and / or chemically bonded to the first composite oxide. Further, the alloy oxide may be in a state of being physically and / or chemically bonded to the second composite oxide. Further, the alloy oxide may be in a state of being physically and / or chemically bonded to the solid solution formed by the first composite oxide and the second composite oxide.

As described above, the positive electrode active material according to the present embodiment can enhance the structural stability by containing the alloy oxide described above, and when such a positive electrode active material is used in a lithium secondary battery. , High temperature storage stability and life characteristics of the positive electrode active material can be improved. Further, the alloy oxide can affect the improvement of the efficiency characteristics of the lithium secondary battery by acting as a pathway of lithium ions in the positive electrode active material.

Further, in some cases, the alloy oxide is present not only in at least a part of the interface between the core and shell particles and the surface of the secondary particles, but also in the internal pores formed inside the secondary particles. can do.

As shown through the above chemical formula 4, the alloy oxide is an oxide in which lithium and a metal element represented by M5 are composited, and the alloy oxide is, for example, Li (W) O. It may be Li (Zr) O, Li (Ti) O, Li (B) O, WO _x , ZrO _x , TiO _x , etc., but the above examples are provided for convenience only for the sake of understanding. However, the alloy oxides defined in the present application are not limited to the above-mentioned examples. Therefore, in the experimental examples described later, the experimental results for some examples of typical alloy oxides represented by the chemical formula 4 will be described for convenience.

In another embodiment, the alloy oxide is an oxide in which at least two metal elements represented by lithium and M5 are combined, or at least two metal elements represented by lithium and M5. Can further contain a complexed oxide. The alloy oxide in which at least two kinds of metal elements represented by lithium and M5 are compounded is, for example, Li (W / Ti) O, Li (W / Zr) O, Li (W / Ti / Zr) O. , Li (W / Ti / B) O and the like, but are not necessarily limited to these.

Further, in this case, it is possible to have a lattice structure in which at least one metal element is doped in the lithium tungsten oxide. That is, the alloy oxide has a lattice structure formed by a lithium tungsten oxide (eg, Li ₂ WO ₄ , Li ₂ W ₂ O ₇ , Li ₄ WO ₅ , Li ₆ WO ₆ or Li ₆ W ₂ O ₉ ). It will have a lattice structure in which a part of the inner tungsten is replaced with a metal element. Here, examples of the metal element that replaces tungsten in the lattice structure include Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, and Ce. , Nd and at least one selected from Gd can be used.

In one embodiment, the alloy oxide can exhibit a concentration gradient that decreases from the surface portion of the secondary particles toward the center portion of the secondary particles. Along with this, the concentration of the alloy oxide can be reduced from the outermost surface of the secondary particles toward the center of the secondary particles.

As described above, the residual lithium present on the surface of the positive electrode active material is effective by showing a concentration gradient in which the alloy oxide decreases from the surface portion of the secondary particles toward the center portion of the secondary particles. It is possible to prevent side reactions due to unreacted residual lithium in advance, and to prevent the alloy oxide from deteriorating the crystallinity in the surface inner region of the positive electrode active material. can. In addition, the alloy oxide can prevent the overall structural collapse of the positive electrode active material during the electrochemical reaction.

In another embodiment, the alloy oxide can include a first alloy oxide represented by the following chemical formula 5 and a second alloy oxide represented by the following chemical formula 6.

[Chemical formula 5]
Li _{h Wi} O _j

(Here, 0 ≦ i ≦ 6, 0 <j ≦ 6, 0 <k ≦ 10).

[Chemical formula 6]
Li _k M6 _l O _m

(here,
M6 is at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd.
0 ≦ k ≦ 6, 0 <l ≦ 6, 0 <m ≦ 10. )

At this time, the first alloy oxide and the second alloy oxide can show a concentration gradient that decreases from the surface portion of the secondary particles toward the center portion of the secondary particles. Along with this, the concentrations of the first alloy oxide and the second alloy oxide can be reduced from the outermost surface of the secondary particles toward the center of the secondary particles.

At this time, the concentration reduction rate of the second alloy oxide is preferably larger than the concentration reduction rate of the first alloy oxide, and the concentration reduction rate of the second alloy oxide is the concentration of the first alloy oxide. By being greater than the rate of decrease, the structural stability of the positive electrode active material, including the alloy oxides, can be maintained. Further, by forming an efficient pathway of lithium ions in the positive electrode active material, it can positively act to improve the efficiency characteristics of the lithium secondary battery.

Further, the alloy oxide can include a third alloy oxide represented by the following chemical formula 7.

[Chemical formula 7]
Li _n W _1-o M7 _{o Op}

(here,
M7 is at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd.
0 ≦ n ≦ 6, 0 <o ≦ 0.50, 0 <p ≦ 6. )

Here, the third alloy oxide can have a lattice structure in which a part of the tungsten in the lattice structure is substituted with M7.

As described above, when the positive electrode containing the positive electrode active material according to various embodiments of the present invention is used as the positive electrode of the lithium secondary battery, the high temperature storage stability and the life characteristics can be further improved.

Lithium Secondary Battery According to still another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector can be provided. Here, the positive electrode active material layer can contain the positive electrode active material according to various examples of the present invention. Therefore, since the positive electrode active material is the same as that described above, a specific description thereof will be omitted for convenience, and only the remaining configurations not described above will be described below.

The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and is not particularly limited, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, aluminum, or stainless steel. A surface-treated steel surface with carbon, nickel, titanium, silver or the like can be used. Further, the positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as a film, a sheet, a wheel, a net, a porous body, a foam, and a non-woven fabric.

The positive electrode active material layer may contain a conductive material and, if necessary, a binder selectively together with the positive electrode active material.

At this time, the positive electrode active material may be contained in a content of 80 to 99 wt%, more specifically, 85 to 98.5 wt% with respect to the total weight of the positive electrode active material layer. When contained within the above content range, it can exhibit excellent volumetric properties, but is not necessarily limited to this.

The conductive material is used to impart conductivity to the electrodes, and can be used without any special limitation as long as it does not cause a chemical change and has electronic conductivity in the constituent battery. It is possible. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; copper, nickel, and the like. Examples thereof include metal powders or metal fibers such as aluminum and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. One type alone or a mixture of two or more types may be used. The conductive material may be contained in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

The binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacryllonerile, carboxymethyl cellulose (CMC), starch, and hydroxypropyl. Cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. However, one of these may be used alone or a mixture of two or more thereof may be used. The binder may be contained in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

The positive electrode can be manufactured by a usual method for manufacturing a positive electrode, except that the positive electrode active material described above is used. Specifically, the above-mentioned positive electrode active material and, optionally, a composition for forming a positive electrode active material layer produced by dissolving or dispersing a binder and a conductive material in a solvent are applied onto a positive electrode current collector, and then dried and dried. It can be manufactured by rolling.

The solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropanol alcohol), N-methylpyrrolidone (NMP), and acetone (acetone). Alternatively, water and the like may be mentioned, and one of these alone or a mixture of two or more thereof may be used. The amount of the solvent used is such that the positive electrode active material, the conductive material and the binder are dissolved or dispersed in consideration of the coating thickness of the slurry and the production yield, and thereafter, the thickness is excellent at the time of coating for the production of the positive electrode. It is sufficient to have a viscosity that can be shown once.

Further, in another embodiment, the positive electrode is obtained by casting the composition for forming a positive electrode active material layer onto another support and then peeling the film from the support onto the positive electrode current collector. It can also be manufactured by lamination.

Further, according to still another aspect of the present invention, an electrochemical device including the above-mentioned positive electrode can be provided. The electrochemical element may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

Specifically, the lithium secondary battery can include a positive electrode, a negative electrode located facing the positive electrode, and a separation membrane and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is the same as that described above, a specific description thereof will be omitted for convenience, and only the remaining configurations not described above will be specifically described below.

The lithium secondary battery can optionally further include a battery container for accommodating the positive electrode, the negative electrode and the electrode assembly of the separation membrane, and a sealing member for sealing the battery container.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and is not particularly limited, for example, copper, stainless steel, aluminum, nickel, titanium, and fired. Surface-treated carbon, copper, stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. Further, the negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities are formed on the surface of the current collector to bond the negative electrode active material. You can also strengthen your power. For example, it can be used in various forms such as a film, a sheet, a wheel, a net, a porous body, a foam, and a non-woven fabric.

The negative electrode active material layer selectively contains a binder and a conductive material together with the negative electrode active material.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, and Si alloys. Metallic compounds capable of alloying with lithium, such as Sn alloys or Al alloys; may be doped and dedoped with lithium, such as SiO _β (0 <β <2), SnO ₂ , vanadium oxide, lithium vanadium oxide. Metal oxides; or composites containing said metallic compounds and carbonaceous materials, such as Si—C complexes or Sn—C complexes, and mixtures of any one or more of these. Can be used. Further, a metallic lithium thin film can also be used as the negative electrode active material. Further, as the carbon material, low crystalline carbon, high crystalline carbon and the like can all be used. Typical examples of low crystalline carbon are soft carbon and hard carbon, and examples of high crystalline carbon are amorphous, plate-like, scaly, spherical or fibrous natural graphite. Or artificial graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber (mesophase platinum based carbon fiber), carbon microspheres (meso-carbon microbeads), liquid crystal pitch (meso-carbon microbeads), liquid crystal pitch. And high temperature pyrolytic carbon such as petroleum or coal tar punctch divided cokes are typical.

The negative electrode active material may be contained in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can be usually added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders are polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-. Examples thereof include diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, graphite such as natural graphite or artificial graphite; acetylene black, etc. Carbon black such as kechen black, channel black, furnace black, lamp black, thermal black; conductive fiber such as carbon fiber and metal fiber; metal powder such as carbon fluoride, aluminum and nickel powder; zinc oxide, potassium titanate Conductive whiskers such as; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

In one embodiment, the negative electrode active material layer is a composition for forming a negative electrode active material layer produced by dissolving or dispersing a negative electrode active material, and selectively a binder and a conductive material in a solvent on a negative electrode current collector. It is manufactured by applying and drying, or the composition for forming the negative electrode active material layer is cast on another support, and then the film obtained by peeling from the support is placed on the negative electrode current collector. It can be manufactured by laminating.

Further, in another embodiment, the negative electrode active material layer is used for forming a negative electrode active material layer produced by selectively dissolving or dispersing a negative electrode active material, and selectively a binder and a conductive material in a solvent on a negative electrode current collector. The composition is applied and dried, or the composition for forming the negative electrode active material layer is cast on another support, and then the film obtained by peeling from the support is laminated on the negative electrode current collector. It can also be manufactured by.

On the other hand, in the lithium secondary battery, the separation film separates the negative electrode and the positive electrode to provide a movement passage for lithium ions, and is usually used as a separation film in the lithium secondary battery. It can be used without any special restrictions, and it is particularly preferable that the electrolyte has a low resistance to ion transfer and an excellent electrolyte moisturizing capacity. Specifically, porous polymer films such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers are polyolefin-based polymers. A porous polymer film produced in 1 or a laminated structure having two or more layers thereof can be used. Further, a normal porous non-woven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like can also be used. Further, in order to ensure heat resistance or mechanical strength, a coated separation membrane containing a ceramic component or a polymer substance can also be used, and can be selectively used in a single-layer or multi-layer structure.

The electrolyte used in the present invention includes an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-like polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the manufacture of a lithium secondary battery. Examples include, but are not limited to, electrolytes.

Specifically, the electrolyte can include an organic solvent and a lithium salt.

The organic solvent can be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; dibutyl ether (dibutyl ether (). Ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethyl carbonate, dimethylcarbon. , Dithylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (ethylene carbonone, EC), propylene carbonate (propylene solvent; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and contains a double-bonded aromatic ring or an ether bond. Can be used) such as nitriles; amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or solvents and the like can be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can enhance the charge / discharge performance of the battery and low-viscosity linear carbonates. Mixtures of system compounds (eg, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferred. In this case, the performance of the electrolytic solution can be excellently exhibited by mixing the cyclic carbonate and the chain carbonate in a volume ratio of about 1: 1 to about 1: 9.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salts are LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ). ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ may be used. The concentration of the lithium salt is preferably used in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can be effectively transferred.

In addition to the electrolyte constituents, the electrolyte is a haloalkylene carbonate type such as difluoroethylene carbonate for the purpose of improving the life characteristics of the battery, suppressing the decrease in the battery capacity, and improving the discharge capacity of the battery. Compound, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene. One or more additives such as glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further contained. At this time, the additive may be contained in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

As described above, the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics. It is also useful in the field of electric vehicles such as hybrid electric batteries (HEVs).

The outer shape of the lithium secondary battery according to the present invention is not particularly limited, but may be cylindrical, square, pouch-shaped, coin-shaped, or the like using a can. In addition, the lithium secondary battery can be used as a battery cell used as a power source for a small device, and can also be preferably used as a unit battery in a medium-sized battery module including a large number of battery cells.

According to still another aspect of the present invention, a battery module containing the lithium secondary battery as a unit cell and / or a battery pack containing the same can be provided.

The battery module or the battery pack is a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (Plug-in Hybrid Electric Vehicle, PHEV); Alternatively, it is used as a power source for medium and large devices of any one or more of power storage systems.

Hereinafter, the present invention will be described in more detail through examples. However, it can be said that these examples are merely for exemplifying the present invention, and it cannot be understood that the scope of the present invention is limited by these examples.

Experimental example 1.
(1) Production of positive electrode active material (Example 1)
A spherical Ni _0.92 Co _0.08 (OH) ₂ hydroxide precursor was synthesized by the co-precipitation method. 25 wt% NaOH and 30 wt% NH ₄ OH in a 1.5 M composite transition metal sulfuric acid aqueous solution in which NiSO _{4.7H 2} O and CoSO _{4.7H 2 O} are mixed in a molar ratio of 92: 8 in a 90 L class reactor. Was put in. The pH in the reactor was maintained at 11.5, the temperature of the reactor at this time was maintained at 60 ° C., and the inert gas N ₂ was charged into the reactor to produce a precursor. I tried not to oxidize. After the completion of the synthetic stirring, washing and dehydration were carried out using a filter press (F / P) equipment to obtain a Ni _0.92 Co _0.08 (OH) ₂ hydroxide precursor.

The hydroxide precursor is mixed with LiOH, which is a Li-containing raw material, and Al ₂ O ₃ , which is an Al-containing raw material, using a mixer, and the temperature rises at 1 ° C. per minute while maintaining the O ₂ atmosphere in the firing furnace. It was heated and maintained at a heat treatment temperature of 650 ° C. for 10 hours, and then naturally cooled. The obtained positive electrode active material was mixed with a W-containing raw material (WO ₃ ) using a mixer. While maintaining the O ₂ atmosphere in the same firing furnace, the temperature was raised at 2 ° C. per minute, maintained at a heat treatment temperature of 600 ° C. for 5 hours, and then naturally cooled. Next, heat treatment and cooling were further performed once under the same conditions as described above. It was confirmed that the positive electrode active material produced in Example 1 had a Li _1.0 Ni _0.902 Co _0.079 Al _0.014 W _0.005 O ₂ composition formula.

(Example 2)
The W-containing raw material (WO ₃ ) and the W-containing raw material (WO 3) so that the positive electrode active material obtained in Example 2 has a composition formula of Li _1.04 Ni _0.897 Co _0.084 Al _0.014 W _0.005 O ₂ . The positive electrode active material was produced by the same method as in Example 1 except that it was mixed with the cobalt raw material (Co (OH) ₂ ).

(Example 3)
The W-containing raw material (W-containing raw material) so that the positive electrode active material obtained in Example 3 has a composition formula of Li _1.04 Ni _0.897 Co _0.079 Al _0.014 W _0.005 Mg _0.005 O ₂ . The positive electrode active material was produced by the same method as in Example 1 except that it was mixed with WO ₃ ) and a magnesium raw material (Mg (OH) ₂ ).

(Example 4)
The W-containing raw material (W-containing raw material) so that the positive electrode active material obtained in Example 4 has a composition formula of Li _1.04 Ni _0.897 Co _0.079 Al _0.014 W _0.005 Mn _0.005 O ₂ . A positive electrode active material was produced in the same manner as in Example 1 except that it was mixed with WO ₃ ) and a manganese raw material (Mn (OH) ₂ ).

(Example 5)
The W-containing raw material (W-containing raw material) so that the positive electrode active material produced in Example 5 has a composition formula of Li _1.04 Ni _0.901 Co _0.079 Al _0.014 W _0.005 Ti _0.001 O ₂ . The positive electrode active material was produced by the same method as in Example 1 except that WO ₃ ) and the Ti-containing raw material (TiO ₂ ) were used.

(Example 6)
The W-containing raw material (W-containing raw material) so that the positive electrode active material produced in Example 6 has a composition formula of Li _1.04 Ni _0.904 Co _0.079 Al _0.014 W _0.005 Zr _0.001 O ₂ . The positive electrode active material was produced by the same method as in Example 1 except that WO ₃ ) and a Zr-containing raw material (ZrO ₂ ) were used instead.

(Example 7)
The positive electrode active material produced in Example 7 has a composition formula of Li _1.04 Ni _0.901 Co _0.078 Al _0.014 W _0.005 Ti _0.001 Zr _0.001 O ₂ . The positive electrode active material was produced by the same method as in Example 1 except that the W-containing raw material (WO ₃ ) and the W and Ti-containing raw materials (TiO ₂ ) and the Zr-containing material were mixed together.

(Comparative Example 1)
Same as Example 1 except that the Li _1.04 Ni _0.907 Co _0.079 Al _0.014 O ₂ positive electrode active material produced in Comparative Example 1 is not mixed with the W-containing raw material (WO ₃ ). The positive electrode active material was produced by the method.

(Comparative Example 2)
Li ₄ NiWO ₆ was synthesized using the solid phase synthesis method. Ni (OH) ₂ , WO ₃ and LiOH · H ₂ O were mixed with a mixer and then heat treated at 1000 ° C. to produce a Li ₄ Ni WO ₆ lithium composite oxide. Li ₄ NiWO ₆ was mixed with 0.5 mol% of the positive electrode active material produced in Comparative Example 1 to produce a positive electrode active material.

(Comparative Example 3)
Li _1.04 Ni _0.907 Co _0.079 Al _0.014 O ₂ positive electrode active material produced in Comparative Example 1 and Li ₂ WO ₄ and Li ₂ W ₂ O ₇ synthesized by using a solid phase synthesis method. After mixing 0.5 mol%, the positive electrode active material was produced by the same method as in Example 1 except that no heat treatment was performed.

(Comparative Example 4)
Li _1.04 Ni _0.907 Co _0.079 Al _0.014 O ₂ positive electrode active material produced in Comparative Example 1 and Li ₄ NiWO ₆ 0.5 mol% synthesized by the solid phase synthesis method were mixed. After that, the positive electrode active material was produced by the same method as in Example 1 except that no heat treatment was performed.

(2) XPS analysis of positive electrode active material XPS analysis was performed on the positive electrode active material produced by Examples and Comparative Examples to confirm whether or not a solid solution was present among the positive electrode active materials. For XPS analysis, Quantum 2000 (Physical Electricals. Inc.) (acceleration voltage: 0.5 to 15 keV, 300 W, energy resolution: about 1.0 eV, minimum analysis area: 10 micro, Sputter rate: 0.1 nm / min) is used. It was done.

FIG. 2 is a graph showing the XPS analysis results for the positive electrode active material produced in Example 1.

Referring to FIG. 2, the W4f _7/2 peak for ^O2- of the oxide of Li _a Ni _b W _{c Od} composition is in the range of 34.0 eV to 35.0 eV, and the W4f _5/2 peak is. , 36.0 eV to 37.0 eV can be confirmed to exist. On the other hand, the W4f _7/2 peak for W ⁶⁺ of the oxide of Li _a W _{c Od} or W _{c Od} composition exists in the range exceeding 35.5 eV, and the W4f _5/2 peak is 37.5 eV. It can be confirmed that it exists in the excess range.

In the case of the W4f spectrum of the positive electrode active material produced according to Example 1, the W4f _7/2 peak exists in the range of 34.0 eV to 35.5 eV, and the W4f _{5 /} is in the range of 36.0 eV to 37.5 eV. It can be confirmed that there are _two peaks. That is, the positive electrode active material produced in Example 1 shows a peak peculiar to Li _a Ni _b W _{c Od} .

Therefore, as shown in FIG. 2, it is manufactured according to Example 1 by confirming that there is a unique peak corresponding to Li _a Ni _b W _{c Od} according to the W4f result among the positive electrode active materials having the NCA composition. The positive electrode active material obtained contains a complex in which an oxide having a Li _a Ni _b W _{c Od} composition and an oxide having a Li _w Ni 1- (x + _{y + z)} Co _x Aly W _z O ₂ composition form a solid solution. You can see that there is.

Table 2 below shows the binding energy sections in which the peaks corresponding to W4f _7/2 and W4f _5/2 of the positive electrode active materials produced in Examples and Comparative Examples are present, respectively.

With reference to the results in Table 2, in the case of Examples 1 to 7, unlike Comparative Example 4, an oxide having a Li _a Ni _b W _{c Od} composition was not added separately. It can be confirmed that the W4f peak corresponding to the oxide of the Li _a Ni _b W _{c Od} composition is observed.

(3) XRD analysis of positive electrode active material X-ray diffraction (XRD) analysis was performed on the positive electrode active material produced in Examples and Comparative Examples, and among the positive electrode active materials, Li _w Ni _{1- (x + y + z)} Co _x Al. It was confirmed whether or not the _y W _z O ₂ and Li _a Ni _b W _{c Od} phases were differently present. XRD analysis was performed using a Bruker D8 Advance diffraction meter (diffractometer) using Cu Kα radiation (1.540598 Å).

3 to 5 are graphs showing the XRD analysis results for the positive electrode active material produced according to Example 1.

Referring to FIG. 3, the compounds contained in the positive electrode active material have diffraction peak characteristics specific to Li _a Ni _b W _c O _d and specific to Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ . It can be confirmed that the typical diffraction peak characteristics are exhibited at the same time.

More specifically, referring to FIGS. 4 and 5, when 2θ is around 18.8 °, the diffraction peak corresponding to the (003) crystal plane of Li _w Ni _{1- (x + y + z) Cox Aly} W _z O ₂ is obtained. It can be confirmed that it is shown. Further, it can be confirmed that 2θ shows a diffraction peak corresponding to the (001) crystal plane of Li ₄ NiWO ₆ at around 18.3 °. That is, the compound contained in the positive electrode active material has diffraction peak characteristics specific to Li _a Ni _b W _{c Od} and Li _w Ni _{1- (x + y + z)} Co _x Al in the region where 2θ is 18 ° to 20 °. Diffraction peak characteristics specific to _y W _z O ₂ are simultaneously shown.

Specific diffraction at the positions of (020) crystal plane, (110) crystal plane, (11-1) crystal plane and (021) crystal plane in the region where 2θ contained in the positive electrode active material is 20 ° to 30 °. It shows a peak, and it can be confirmed that this is a diffraction peak corresponding to Li _a Ni _b W _{c Od} .

Further, referring to FIGS. 3 and 5, the compound contained in the positive electrode active material when 2θ is around 44.5 ° is a (104) crystal of Li _w Ni 1- (x + _{y + z)} Co _x Aly W _z O ₂ . It can be confirmed that the diffraction peak corresponding to the plane is shown and that the diffraction peak corresponding to the (20-2) crystal plane of Li ₄ NiWO ₆ is shown near 2θ of 43.2 °.

Along with this, when the results of FIGS. 3 to 5 are put together, the compounds contained in the positive electrode active material have diffraction peak characteristics specific to Li _a Ni _b W _{c Od} and Li _w Ni _{1- ( x + y + z)} By simultaneously showing the diffraction peak characteristics specific to Co _x Al _y W _z O ₂ , the chemical formula Li _a Ni _b W _c O _d -Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ It can be confirmed that the solid solution is represented.

At the same time, the positive electrode active materials produced by Examples 2 to 7 all show a diffraction peak pattern specific to the solid solution and the lithium alloy oxide, but in the case of the positive electrode active material produced by Comparative Example 1, Only the diffraction peak pattern corresponding to the Li _w Ni 1- (x + _{y + z)} Co _x Alloy O ₂ composition was detected.

On the other hand, in the case of the positive electrode active material produced by Comparative Example 2 and Comparative Example 3, the positive electrode produced by Comparative Example 4 did not show a diffraction peak specific to _{Lia Nib W c Od as a} result of XRD analysis. In the case of the active material, a diffraction peak pattern similar to that of the positive electrode active material produced in Example 1 was shown.

In the case of the positive electrode active material produced by Comparative Example 4, the oxide of Li _a Ni _b W _{c Od} composition is simply mixed with the oxide of Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ composition. The diffraction peaks caused by each of Li _a Ni _b W _{c Od} and Li _w Ni _{1- (x + y + z) Cox Aly} W _z O ₂ were simultaneously detected as they existed in the above state, and Comparative Example 4 It does not mean that Li _a Ni _b W _{c Od} and Li _w Ni 1- (x + _{y + z)} Co _x Aly W _z O ₂ which are constituents of the positive electrode active material produced by the above form a solid solution.

Further, X-ray diffraction (XRD) analysis is performed on the positive electrode active materials produced in Examples 5 to 7 to confirm whether or not alloy oxides and alloy oxides are present among the positive electrode active materials. did. XRD analysis was performed using a Bruker D8 Advance diffraction meter (diffractometer) using Cu Kα radiation (1.540598 Å).

6 to 8 are graphs showing the XRD analysis results for the positive electrode active material produced by Examples 5 to 7.

Referring to FIG. 6, characteristic peaks corresponding to the alloy oxide Li ₄ WO ₅ among the positive electrode active materials produced in Example 5 were confirmed, and in particular, the (220) peak was not shifted. However, as the (111) and (200) peaks are specifically shifted to the low alloy side, some of the tungsten in the lattice structure formed by Li ₄ WO ₅ is Ti. It was confirmed that there was a heterogeneous alloy oxide substituted with.

Further, referring to FIG. 7, a characteristic peak corresponding to the alloy oxide Li ₄ WO ₅ among the positive electrode active materials produced in Example 6 was confirmed, and in particular, (111), (200) and (220) and (220) were confirmed. ) A heterogeneous alloy oxide in which some of the tungsten in the lattice structure formed by Li ₄ WO ₅ is replaced by Zr as the peak is specifically shifted to the low angle side. Confirmed that exists.

With reference to FIG. 8, it can be confirmed that the positive electrode active material produced according to Example 7 has an NCA composition, and at the same time, Li ₄ WO ₅ and Li ₆ WO ₆ in the positive electrode active material can be confirmed. , LiTiO ₂ , Li ₄ TiO ₄ and Li ₄ ZrO ₄ were confirmed to have peaks.

(5) Measurement of unreacted lithium of the positive electrode active material The measurement of unreacted lithium with respect to the positive electrode active material produced by Examples and Comparative Examples was performed with 0.1 M HCl used until pH 4 was reached by pH titration. Was measured by the amount of. First, 5 g of each positive active substance was placed in 100 ml of DIW, stirred for 15 minutes, filtered, and 50 ml of the filtered solution was taken, and then 0.1 M HCl was added to measure the amount of HCl consumed due to pH change. Then, Q1 and Q2 were determined, and unreacted LiOH and Li ₂ CO ₃ were calculated through this.

M1 = 23.95 (LiOH Molecular weight)
M2 = 73.89 (Li ₂ CO ₃ Molecular weight)
SPL Size = (Simple weight x Solution Weight) / Water Weight
LiOH (wt%) = [(Q1-Q2) x C x M1 x 100] / (SPL Size x 1000)
Li ₂ CO ₃ (wt%) = [2 x Q2 x C x M2 / 2 x 100] / (SPL Size x 1000)

The measurement results of unreacted lithium measured through the above formula are shown in Table 3 below.

With reference to the results in Table 3, the positive electrode active materials produced by Examples 1 to 7 had a significantly reduced amount of residual lithium as compared with the positive electrode active materials produced by Comparative Examples 1 to 4. You can confirm that. In particular, an oxide having a Li _a W _{c Od} , W _c O _d or Li _a Ni _b W _{c Od} composition is combined with a composite oxide having a Li ^w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ composition. In the case of Comparative Example 2 to Comparative Example 4 in which each is simply mixed, the amount of residual lithium is sufficient as compared with the positive electrode active material (Comparative Example 1) having a simple Li _w Ni _{1- (x + y + z) Cox} Al _y W _z O ₂ composition. It can be confirmed that it does not decrease.

Experimental example 2.
(1) Production of Lithium Secondary Battery 94 wt% of positive electrode active material, 3 wt% of carbon black, and 3 wt% of PVDF binder produced by Examples and Comparative Examples were added to 30 g of N-methyl-2pyrrolidone (NMP), respectively. It was dispersed to produce a positive electrode slurry. The positive electrode slurry was applied to and dried on an aluminum (Al) thin film which is a positive electrode current collector having a thickness of 15 μm, and a roll press was carried out to produce a positive electrode. The loading level of the positive electrode was 10 mg / cm ² , and the electrode density was 3.2 g / cm ³ .

Metallic lithium was used as a counter electrode with respect to the positive electrode, and ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed as an electrolytic solution in a volume ratio of 2: 4: 4. It was produced by adding 1.15 M LiPF ₆ to the solvent.

A battery assembly was formed by interposing a separator made of a porous polyethylene (PE) film between the positive electrode and the negative electrode, and the electrolytic solution was injected to produce a lithium secondary battery (coin cell).

(2) Evaluation of capacity characteristics of lithium secondary battery The lithium secondary battery (coin cell) manufactured above is charged at 25 ° C. with a constant current (CC) of 0.15 C until it reaches 4.25 V. The battery was charged at a constant voltage (CV) of 4.25 V, and the first charge was performed until the charging current reached 0.05 mAh. After that, after leaving it for 20 minutes, it was discharged at a constant current of 0.1 C until it became 3.0 V, and the discharge capacity in the first cycle was measured. The charge capacity, discharge capacity, and charge / discharge efficiency at the time of the first charge / discharge are shown in Table 4 below.

With reference to the results in Table 4, the lithium secondary battery using the positive electrode active material produced by Examples 1 to 7 is the lithium using the positive electrode active material produced by Comparative Examples 1 to 4. It can be confirmed that the charging / discharging efficiency and the capacity characteristics are improved as compared with the secondary battery. In particular, the composite oxide of Li _a W _{c Od} and W _c O _d , Li _a Ni _b W _{c Od} composition is combined with the composite oxide of Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ composition. In the case of _{Comparative Example 2} to _{Comparative Example 4} in which each of them was simply mixed, the charge / discharge efficiency and the charge / discharge efficiency and 4. Although the 0C / 0.2C rate characteristics were improved, the composite oxide of Li _a Ni _b W _{c Od} composition and the composite oxide of Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ composition were solid solutions. It can be confirmed that the performance is insufficient as compared with the examples forming the above.

Further, as described above, the lithium secondary battery using the positive electrode active material produced by Examples 1 to 7 containing the solid solution has improved electrochemical characteristics as compared with Comparative Examples, and at the same time, particularly compared. Unlike Example 2 to Comparative Example 4, the difficulty level and the process cost of the manufacturing process can be reduced by not adding the W-containing oxide separately.

(3) Evaluation of Stability of Lithium Secondary Battery The driving voltage range of 3.0 to 4.25V at a constant current (CC) of 1C at 25 ° C for the lithium secondary battery (coin cell) manufactured above. Charging / discharging was carried out 100 times in the room. As a result, after 100 times of charging and discharging at room temperature, the cycle capacity retention rate (capacity retention), which is the ratio of the discharge capacity at the 100th cycle to the initial capacity, was measured.

In addition, in order to confirm the high temperature storage characteristics of the lithium secondary battery, the battery charged and discharged at 25 ° C. is charged with 100% SOC as a reference to measure the resistance, and then stored at 60 ° C. for 7 days, and then the resistance is measured. The change width of the resistance was confirmed.

The measurement results are shown in Table 5 below.

With reference to the results in Table 5, the lithium secondary battery using the positive electrode active material produced by Examples 1 to 7 is the lithium using the positive electrode active material produced by Comparative Examples 1 to 4. It can be confirmed that the capacity retention rate is superior to that of the secondary battery and the resistance change width before and after high temperature storage is small. In particular, a composite oxide having a Li _a Ni _b W _{c Od} , Li _a W _{c Od} and W _{c Od} composition and a composite oxide having a Li _w Ni _{1- (x + y + z)} Co _x Al _y W _z O ₂ composition. In the case of Comparative Examples 2 to 4 in which each of them was simply mixed, the capacity retention rate and the resistance characteristics were improved as compared with the positive electrode active material (Comparative Example 1) having a simple Li _w Ni 1- (x + _{y + z)} Co _x Aly W _z O ₂ composition. However, compared to the examples in which the composite oxide of Li _a Ni _b W _{c Od} composition and the composite oxide of Li _w Ni 1- (x + _{y + z)} Co _x Aly W _z O ₂ composition form a solid solution. It can be confirmed that the performance is insufficient.

Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art concerned can add, change, or delete components within the range not departing from the idea of the present invention described in the claims. Alternatively, the present invention can be modified and changed in various ways by addition or the like, and it can be said that this is also included in the scope of the rights of the present invention.

Claims (14)

It contains a first composite oxide capable of sucking and releasing lithium; and a second composite oxide present on at least a portion of the surface of the first composite oxide;
The first composite oxide and the second composite oxide exist in a state of forming a solid solution, and are present.
The second composite oxide is represented by the following chemical formula 1 as a positive electrode active material:
[Chemical formula 1]
Li _a M1 _b M2 _{c Od}
(here,
M1 is at least one selected from Ni, Mn, Co, Cu, Nb, Mo, Al, Zn, Mg, Ce and Sn.
M2 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
M1 and M2 are different from each other
0 ≦ a ≦ 6, 0 <b ≦ 2, 0 <c ≦ 2, 4 ≦ d ≦ 8. ) The positive electrode active material according to claim 1, wherein M1 is at least one selected from Mn, Mg, Co and Ni. The positive electrode activity according to claim 1, wherein the second complex oxide has at least one crystal structure selected from a monoclinic system, a triclinic system, and a cubic system. material. The positive electrode active material is
It is formed of one or more core-shell particles containing a core containing the first composite oxide; and a shell layer present on at least a portion of the surface of the core.
The positive electrode active material according to claim 1, wherein the second composite oxide existing in a state of forming a solid solution with the first composite oxide is present in at least a part of the shell layer. The positive electrode active material according to claim 4, wherein the second composite oxide present in the shell layer is a lithium-rich metal oxide. The positive electrode active material according to claim 4, wherein the first composite oxide is represented by the following chemical formula 2.
[Chemical formula 2]
Li _w Ni _{1- (x + y + z)} Co _x M3 _y M4 _z O ₂
(here,
M3 is at least one selected from Mn and Al,
M4 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
0.5 ≦ w ≦ 1.5, 0.01 ≦ x ≦ 0.50, 0.01 ≦ y ≦ 0.20, 0.001 ≦ z ≦ 0.20. ) The positive electrode active material according to claim 4, wherein the positive electrode active material includes the core-shell particles and secondary particles formed by aggregating the core-shell particles. The positive electrode active material according to claim 4, wherein the solid solution is represented by the following chemical formula 3.
[Chemical formula 3]
Li _a M1 _b M2 _{c Od} -Li _w Ni _{1- (x + y + z)} Co _x M3 _y M4 _z O ₂
(here,
M1 is at least one selected from Ni, Mn, Cu, Nb, Mo, Al, Zn, Mg, Ce and Sn.
M2 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
M3 is at least one selected from Mn and Al,
M4 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. ,
M1 and M2 are different from each other
0 ≦ a ≦ 6, 0 <b ≦ 2, 0 <c ≦ 2, 4 ≦ d ≦ 8
0.5 ≦ w ≦ 1.5, 0.01 ≦ x ≦ 0.50, 0.01 ≦ y ≦ 0.20, 0.001 ≦ z ≦ 0.20. ) The positive electrode active material according to claim 8, wherein M2 is the same as a part of M4 or M4. The positive electrode active material according to claim 8, wherein the peak corresponding to W4f _7/2 exists at 35.5 eV or less at the time of XPS (X-ray photoelectron spectroscopy) analysis of the solid solution. The positive electrode active material according to claim 8, wherein the peak corresponding to W4f _5/2 exists in the range of 36.0 eV to 37.5 eV at the time of XPS analysis on the lithium composite oxide. Further comprising a coating layer covering at least a portion of the secondary particles
The positive electrode active material according to claim 7, wherein the coating layer contains an alloy oxide represented by the following chemical formula 4.
[Chemical formula 4]
Li _e M5 _{f Og}
(here,
M5 is at least one selected from Mn, Al, Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd. And
0 ≦ e ≦ 6, 0 <f ≦ 6, 0 <g ≦ 10. ) The positive electrode active material according to any one of claims 1 to 12;
A positive electrode slurry composition comprising a conductive material; and a binder; A lithium secondary battery including a positive electrode formed by coating a current collector with the positive electrode slurry composition according to claim 13.

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